Piezoelectric ceramic materials

ABSTRACT

A piezoelectric ceramic material composed of a ternary solid solution of Pb(Ni1/3Nb2/3)O3 - PbTiO3 - PbZrO3 having the composition within an area encircled by lines connecting points A(15 mol % of Pb(Ni1/3Nb170 )O3, 45 mol % of PbTiO3 and 40 mol % of PbZrO3), F(40 mol % of Pb(Ni166 Nb2/3)O3, 30 mol % of PbTiO3 and 30 mol % of PbZrO3), C(51 mol % of Pb(Ni1/3Nb2/3)O3, 24 mol % of PbTiO3 and 25 mol % of PbZrO3), G(45 mol % of Pb(Ni1/3Nb2/3)O3, 35 mol % of PbTiO3 and 20 mol % of PbZrO3), H(40 mol % of Pb(Ni1/3Nb170 )O3, 40 mol % of PbTiO3, and 20 mol % of PbZrO3) and I(30 mol % of Pb(Ni1/3Nb2/3)O3, 45 mol % of PbTiO3 and 25 mol % PbZrO3). And at least one additive selected from the group consisting of Sb2O3, Nb2O5, Bi2O3, La2O3, WO3 is added to the ternary solid solution in an amount of 0.1 to 1.0 weight % of the ternary solid solution.

This is a continuation of application Ser. No. 810,226, filed Dec. 17,1985 which was abandoned upon the filing hereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to piezoelectric ceramic materials which areeffectively utilizable in various types of actuators and which arecomposed of ternary solid solutions having a fundamental composition ofPb(Ni_(1/3) Nb_(2/3))O₃ -PbTiO₃ -PbZrO₃.

2. Description of the Prior Art

Piezoelectric ceramic materials used in actuators should have variouscharacteristics such as a high piezoelectric constant, a high Curiepoint and high mechanical strength. One of piezoelectric materials whichhave been most widely used at present is a piezoelectric ceramicmaterial composed of a ternary solid solution of Pb(Ni_(1/3) Nb_(2/3))O₃-PbTiO₃ -PbZrO₃. Many studies have been made on the above ceramicmaterial in order to further improve the characteristics mentionedabove. For instance, in order to improve the mechanical strength, therewere proposed ceramic materials in Japanese Examined Patent PublicationNo. Sho 46-43062 in which a small amount of ZrSiO₄ was added to theternary solid solution of Pb(Ni_(1/3) Nb_(2/3))O₃ -PbTiO₃ -PbZrO₃.

The improvement in strength of piezoelectric ceramic materials is neededespecially when thin plates of piezoelectric ceramic materials are usedin ultrasonic transducer elements or circuit elements. However, whenthis plates of piezoelectric materials are laminated for use asactuators, it is desirable to increase a degree of displacement ofpiezoelectric ceramic materials upon application of an electric field byincreasing the piezoelectric constant of the materials rather than toimprove the mechanical strength thereof.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to providepiezoelectric ceramic materials composed of ternary solid solutionshaving a fundamental composition of Pb(Ni_(1/3) Nb_(2/3))O₃ -PbTiO₃-PbZrO₃ and having largely improved piezoelectric constants.

The piezoelectric ceramic material of the present invention is composedof a ternary solid solution of Pb(Ni_(1/3) Nb_(2/3))O₃ -PbTiO₃ -PbZrO₃having the composition within an area encircled by lines connectingpoints A(15 mol% of Pb(Ni_(1/3) Nb_(2/3))O₃, 45 mol% of PbTiO₃ and 40mol% of PbZrO₃), F(40 mol% of Pb(Ni_(1/3) Nb_(2/3))O₃, 30 mol% of PbTiO₃and 30 mol% of PbZrO₃), C(51 mol% of Pb(Ni_(1/3) Nb_(2/3))O₃, 24 mol% ofPbTiO₃ and 25 mol% of PbZrO₃), G(45 mol% of Pb(Ni_(1/3) Nb_(2/3))O₃, 35mol% of PbTiO₃ and 20 mol% of PbZrO₃), H(40 mol% of Pb(Ni_(1/3) Nb_(2/3)O₃, 40 mol% of PbTiO₃ and 20 mol% of PbZrO₃) and I(30 mol% ofPb(Ni_(1/3) Nb_(2/3))O₃, 45 mol% of PbTiO₃, and 25 mol% of PbZrO₃). Andat least one additive selected form the group consisting of Sb₂ O₃, Nb₂O₅ , Bi₂ O₃, La₂ O₃, WO₃ is added to the ternary solid solution in anamount of 0.1 to 1.0 weight% of the ternary solid solution.

The piezoelectric ceramic materials according to the present inventionhave a piezoelectric constant as high as about 450×10⁻¹² to 600×10⁻¹²m/V. Upon application of an electric field, a great degree ofdisplacement can be obtained, so that the piezoelectric ceramicmaterials of the invention can be effectively utilized as piezoelectricmaterials for various actuators such as of injectors for internalcombustion engines of vehicles.

Furthermore, the piezoelectric ceramic materials according to thepresent invention have a sintered density of about 7.70 g/cm³ or moreand a curie temperature of about 160° C. or more so that sufficientlylarge mechanical strength and good heat resistance can be obtained.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a triangular compositional diagram of the fundamentalcomposition of the piezoelectric ceramic materials.

DETAILED DESCRIPTION OF THE EMBODIMENT

The piezoelectric ceramic materials of the present invention areprepared, for example, by powdered metal techniques. More particularly,starting materials for these ceramic materials such as PbO, TiO₂, ZrO₂,NiO, Nb₂ O₅, Sb₂ O₃, Bi₂ O₃, TaO₃, La₂ O₃, WO₃ and the like are weighedin predetermined ratios and mixed such as in a wet ball mill. Theresulting mixture is dried, calcined at temperatures of 700° to 900° C.for 3 to 10 hours and again mixed in the wet ball mill. After drying,there is obtained an intended powder.

To the powder obtained above is added a binder such as water orpolyvinyl alcohol, followed by press molding under pressure of 300 to1000 Kg/cm² and sintering at a temperature of 1200° to 1300° C. for 1 to3 hours to obtain moldings of a columnar form having a diameter of 5 mmand a length of 8 mm.

The columns are polished on the surfaces thereof, after which electrodesare formed at opposite side ends thereof by a known method. Theelectrode-formed column is placed in an insulating oil such as siliconoil of 20° to 100° C. and a D.C. electric field of 20 to 30 KV/cm isapplied across the electrodes for 6 to 60 minutes for polarization.Thereafter, the polarized column is aged at 120° C. for 1 hour andcooled down to normal temperatures to obtain a sample for measurement.

The piezoelectronic constant d₃₃ of the sample is determined accordingto the following equation (1), in which k₃₃, ε₃₃ and S₃₃ are obtainedaccording to the equations (2) (3) and (4), respectively.

    d.sub.33 =k.sub.33 √ε.sub.33 ·S.sub.33 (1)

    1/(k.sub.33).sup.2 =0.405×fr/(fa-fr)+0.81            (2)

    ε.sub.33 =C×l/S                              (3)

    1/S.sub.33 =4ρ·fa.sup.2 ·l.sup.2 (1-k.sub.33.sup.2) (4)

in which l is a length (m) of the sample, S is an area (m²) of the endsurface of the sample, C is an electrostatic capacitance (F) whenmeasured at 1 KHz by the use of a LCR meter, ρ is a density (Kg/m³), andfa and fr are, respectively, antiresonance and resonance frequencies(Hz). These are measured by known methods, respectively. And k₃₃ is anelectromechanical coupling coefficient.

Table shows the contents and characteristics of samples made in theprocedure as described above.

In Examples 1 to 6, the content of Pb(Ni_(1/3) Nb_(2/3))O₃ isintentionally changed.

As the content of Pb(Ni_(1/3) Nb_(2/3))O₃ is increased, the obtainedpiezoelectric constant is increased, the sintered density becomes largeand the mechanical strength is also improved, but the curie temperatureis decreased.

In this case, Examples 5 and 6 are excluded from the ceramic materialsaccording to the present invention since Example 5 exhibits too smallpiezoelectric constant and Example 6 exhibits too low curie temperature.

In Examples 7 through 16, the content of each of PbTiO₃ and PbZrO₃ isintentionally changed and accordingly the content of Pb(Ni_(1/3)Nb_(2/3))O₃ is also changed.

In Examples, 2, 7, 13 and 14 of which the content of Pb(Ni_(1/3)Nb_(2/3))O₃ is substantially the same as one another, the piezoelectricconstant is lowered as the difference between the content of PbTiO₃ andPbZrO₃ is increased (Examples 13 and 14). So, Examples 13 and 14 areexcluded from the ceramic materials according to the present invention.

And as compared with Examples 10 and 12, in Examples 15 and 16, thesintered density, or the piezoelectric constant becomes lower. So,Examples 15 and 16 are excluded from the ceramic materials according tothe present invention.

Examples 17 through 21 of which the composition is largely changed fromone another exhibit desirable results on the sintered density, thepiezoelectric constant and the curie temperature.

The attached triangular compositional diagram shows the composition ofeach of Examples 1 through 21.

As is clear from the triangular compositional diagram, the compositionsof Examples 1 through 4 and 9 through 12, each exhibiting desirablesintered density and curie temperature and a large piezoelectricconstant of not less than about 450×10⁻¹² m/V, exist within the areaencircled by lines connecting points A, F, C, G, H and I whichcorrespond to the compositions of Examples 1, 10, 19, 4, 12 and 9,respectively.

And Examples 5, 6, 13 through 16 excluded from the ceramic materialsaccording to the present invention exist outside this area.

In Examples 22 to 26, the basic composition of each Example is the sameas that of Example 2 and the content of Sb₂ O₃ as an additive ischanged.

When the content of Sb₂ O₃ is too small, sufficiently large sintereddensity cannot be obtained (Example 25) and when the content of Sb₂ O₃is too large, the piezoelectric coefficient is lowered (Example 26).

These data show that the preferable content of Sb₂ O₃ is 0.1 to 1.0weight%.

And the piezoelectric constant has a peak value when the content of Sb₂O₃ is in the vicinity of 0.5 weight% (Example 2).

When the content of Sb₂ O₃ is over 0.5 weight%, the added Sb₂ O₃ is notcompletely dissolved in the solid solution but part of the added Sb₂ O₃is separated from the solid solution. This results in the piezoelectricconstant being lowered.

In Examples 27 through 39, other additives than Sb₂ O₃ are employed inthe amount of 0.5 to 0.6 weight%.

When one of additives for soft materials such as Nb₂ O₅, Bi₂ O₃, La₂ O₃and WO₃, a mixture of these additives or a mixture of these additive andSb₂ O₃ is employed, the desirable sintered density, curie temperatureand piezoelectric constant can be obtained (Examples 27 through 37). Butwhen additives for hard materials, such as MnO₂, and Fe₂ O₃ is employed,sufficiently large piezoelectric constants cannot be obtained (Examples38 and 39).

From the above experimental results it is clear that the ceramicmaterials composed of ternary solid solutions of Pb(Ni_(1/3) Nb_(2/3))O₃-PbTiO₃ -PbZrO₃ having the compositions within the area encircled by thelines connecting points A, F, C, G, H and I in a triangularcompositional diagram, and including 0.1 to 1.0 weight% of at least onekind of additive selected from the group consisting of Sb₂ O₃, Nb₂ O₅,Bi₂ O₃, La₂ O₃ and WO₃ have excellent mechanical strength and a highcurie temperature, and an especially desirable piezoelectric constant.

When the content of Pb(Ni_(1/3) Nb_(2/3))O₃ is constant and the contentof PbTiO₃ and PbZrO₃ is outside the above described area, desiredpiezoelectric constants cannot be obtained due to the decrease insintered density and specific inductive capacity. (Examples 13, 14, 15and 16).

When the content of Pb(Ni_(1/3) Nb_(2/3))O₃ is increased, the sintereddensity and the piezoelectric constant become larger but the curietemperature remarkably drops (Example 6).

When the content of Pb(Ni_(1/3) Nb_(2/3))O₃ is decreased, the sintereddensity becomes smaller and the mechanical strength is lowered (Example5).

When the content of the above described additives is not more than 0.1weight%, the sintered density becomes small (Example 25) and when notless than 2.0 weight%, part of the additives separates from the solidsolution. This results in the electromechanical coupling coefficient k₃₃being decreased and accordingly the piezoelectric constant being lowered(Example 26).

The piezoelectric materials having the above described properties can besuitably used as the materials for actuators.

                                      TABLE                                       __________________________________________________________________________                                   Sintered                                                                          Specific                                                                           Piezo-electric                                                                        Curie                               X    Y    Z    C        Density                                                                            Inductive                                                                          Constant                                                                              Point                         Sample No.                                                                          (mol %)                                                                            (mol %)                                                                            (mol %)                                                                            (weight %)                                                                             (g/cm.sup.3)                                                                       Capacity                                                                           (× 10.sup.-12                                                                   (°C.)                  __________________________________________________________________________    XPb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 --YPbTiO.sub.3 --ZPbZrO.sub.3 + C            1    15   45   40   Sb.sub.2 O.sub.3                                                                   0.5 7.70 1920 469     300                            2    24   42   34   Sb.sub.2 O.sub.3                                                                   0.5 7.92 2800 571     260                            3    35   35   30   Sb.sub.2 O.sub.3                                                                   0.5 7.94 3350 546     200                            4    45   35   20   Sb.sub.2 O.sub.3                                                                   0.5 8.01 4620 580     165                            5     5   50   45   Sb.sub.2 O.sub.3                                                                   0.5 7.22 1530 320     340                            6    55   30   15   Sb.sub.2 O.sub.3                                                                   0.5 8.02 6770 482     120                            7    24   32   44   Sb.sub.2 O.sub.3                                                                   0.5 7.78 2560 420     230                            8    30   32   38   Sb.sub.2 O.sub.3                                                                   0.5 7.80 2760 448     210                            9    30   45   25   Sb.sub.2 O.sub.3                                                                   0.5 7.81 2890 457     240                           10    40   30   30   Sb.sub.2 O.sub.3                                                                   0.5 7.90 3270 497     180                           11    45   30   25   Sb.sub.2 O.sub.3                                                                   0.5 7.96 4040 540     170                           12    40   40   20   Sb.sub.2 O.sub.3                                                                   0.5 7.91 3960 530     190                           13    22   23   55   Sb.sub.2 O.sub.3                                                                   0.5 7.50 1630 375     210                           14    22   55   23   Sb.sub.2 O.sub.3                                                                   0.5 7.56 1690 382     300                           15    40   23   37   Sb.sub.2 O.sub.3                                                                   0.5 7.73 1700 410     150                           16    40   47   13   Sb.sub.2 O.sub.3                                                                   0.5 7.77 1670 391     210                           17    10   48   42   Sb.sub.2 O.sub.3                                                                   0.5 7.53 1720 402     320                           18    17   30   53   Sb.sub.2 O.sub.3                                                                   0.5 7.51 1700 398     250                           19    51   24   25   Sb.sub.2 O.sub.3                                                                   0.5 7.89 3880 530     160                           20    50   35   15   Sb.sub.2 O.sub.3                                                                   0.5 7.87 3790 420     170                           21    31   48   21   Sb.sub.2 O.sub.3                                                                   0.5 7.60 2230 406     240                           22    24   42   34   Sb.sub.2 O.sub.3                                                                   0.1 7.83 2430 462     270                           23    24   42   34   Sb.sub.2 O.sub.3                                                                   1.0 7.94 2830 527     260                           24    24   42   34   Sb.sub.2 O.sub. 3                                                                  2.0 7.89 2990 410     250                           25    24   42   34   Sb.sub.2 O.sub.3                                                                   0   7.68 2110 428     270                           26    24   42   34   Sb.sub.2 O.sub.3                                                                   2.5 7.78 3120 365     250                           27    24   42   34   Nb.sub.2 O.sub.5                                                                   0.5 7.90 2780 552     260                           28    24   42   34   Bi.sub.2 O.sub.3                                                                   0.5 7.89 2770 570     260                           29    24   42   34   aO.sub.3                                                                           0.5 7.93 2780 571     260                           30    24   42   34   La.sub.2 O.sub.3                                                                   0.5 7.91 2830 563     260                           31    24   42   34   WO.sub.3                                                                           0.5 7.88 2760 560     260                           32    24   42   34   Sb.sub.2 O.sub.3                                                                   0.25                                                                              7.92 2810 573     260                                                La.sub.2 O.sub.3                                                                   0.25                                                33    24   42   34   Sb.sub.2 O.sub.3                                                                   0.2 7.90 2810 568     260                                                Bi.sub.2 O.sub.3                                                                   0.2                                                                      WO.sub.3                                                                           0.2                                                 34    24   42   34   TaO.sub.3                                                                          0.2 7.90 2800 573     260                                                La.sub.2 O.sub.3                                                                   0.2                                                                      WO.sub.3                                                                           0.2                                                 ZPb(Ni.sub.1/2 Nb.sub.2/3)O.sub.3 --YPbTiO.sub.3 --XPbZrO.sub.3 + C           35    24   42   34   Sb.sub.2 O.sub.3                                                                   0.1 7.89 2790 570     300                                                Nb.sub.2 O.sub.5                                                                   0.1                                                                      Bi.sub. 2 O.sub.3                                                                  0.1                                                                      TaO.sub.3                                                                          0.1                                                                      La.sub.2 O.sub.3                                                                   0.1                                                                      WO.sub.3                                                                           0.1                                                 36    24   42   34   Sb.sub.2 O.sub.3                                                                   0.1 7.90 2780 568     260                                                Bi.sub.2 O.sub.3                                                                   0.1                                                                      TaO.sub.3                                                                          0.1                                                                      La.sub.2 O.sub.3                                                                   0.1                                                                      WO.sub.3                                                                           0.1                                                 37    24   42   34   Sb.sub.2 O.sub.3                                                                   0.1 7.90 2800 566     260                                                Nb.sub.2 O.sub.3                                                                   0.1                                                                      Bi.sub.2 O.sub.3                                                                   0.1                                                                      TaO.sub.3                                                                          0.1                                                                      La.sub.2 O.sub.3                                                                   0.1                                                 XPb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 --YPbTiO.sub.3 --ZPbZrO.sub.3 + C           38    24   42   34   MnO.sub.2                                                                          0.5 7.90 1850 388     260                           39    24   42   34   Fe.sub.2 O.sub.3                                                                   0.5 7.86 1790 368     260                           __________________________________________________________________________

What is claimed is:
 1. A piezoelectric ceramic material consisting ofaternary solid solution of Pb(Ni_(1/3) Nb_(2/3))O₃ -PbTiO₃ -PbZrO₃ havingthe composition within an area encircled by lines connecting points:A(15 mol % of Pb(Ni_(1/3) Nb_(2/3))O₃, 45 mol % of PbTiO₃ and 40 mol %of PbZrO₃), F(40 mol % of Pb(Ni_(1/3) Nb_(2/3))O₃, 30 mol % of PbTiO₃and 30 mol % PbZrO₃), C(51 mol % of Pb(Ni_(1/3) Nb_(2/3))O₃, 24 mol % ofPbTiO₃ and 25 mol % of PbZrO₃, G(45 mol % of Pb(Ni_(1/3) Nb_(2/3))O₃, 35mol % PbTiO₃ and 20 mol % of PbZrO₃, H(40 mol % of Pb(Ni_(1/3)Nb_(2/3))O₃, 40 mol % of PbTiO₃ and 20 mol % of PbZrO₃) and I(30 mol %of Pb(Ni_(1/3) Nb_(2/3))O₃, 45 mol % of PbTiO₃, and 25 mol % of PbZrO₃);and Sb₂ O₃ as an additive in an amount of 0.1 to 1.0 weight % of theternary solid solution, said piezoelectric ceramic material having apiezoelectric constant of not less than 450×10⁻¹² m/V.
 2. Apiezoelectric ceramic material according to claim 1, wherein thecomposition of the ternary solid solution is about 24 mol % ofPb(Ni_(1/3) Nb_(2/3))O₃, about 42 mol % of PbTiO₃ and about 34 mol % ofPbZrO₃.
 3. A piezoelectric ceramic material according to claim 1,wherein the at least one additive is added to the ternary solid solutionin an amount of about 0.5 weight %.
 4. A piezoelectric ceramic materialaccording to claim 1, wherein said piezoelectric ceramic material has aCurie point of not less than 160° C.
 5. A piezoelectric ceramic materialaccording to claim 1, wherein said piezoelectric ceramic material has asintered density of not less than 7.70 g/cm³.
 6. A piezoelectric ceramicmaterial consisting ofa ternary solid solution of Pb(Ni_(1/3)Nb_(2/3))O₃ -PbTiO₃ -PbZrO₃ having the composition within an areaencircled by lines connecting points: C(51 mol % of Pb(Ni_(1/3)Nb_(2/3))O₃, 24 mol % mol % of PbTiO₃ and 25 mol% of PbZrO₃), G(45 mol %of Pb(Ni_(1/3) Nb_(2/3))O₃, 35 mol % PbTiO₃ and 20 mol % of PbZrO₃),H(40 mol % of Pb(Ni_(1/3) Nb_(2/3))O₃, 40 mol % of PbTiO₃ and 20 mol %of PbZrO₃), J(24 mol % of Pb(Ni_(1/3) Nb_(2/3))O₃, 42 mol % of PbTiO₃and 34 mol % of PbZrO₃), K(35 mol % of Pb(Ni_(1/3) Nb_(2/3))O₃, 35 mol %of PbTiO₃ and 30 mol % of PbZrO₃); and Sb₂ O₃ as an additive in anamount of 0.5 to 1.0 weight % of the ternary solid solution, saidpiezoelectric ceramic material having a piezoelectric constant of notless than 500×10⁻¹² m/V.
 7. A piezoelectric ceramic material accordingto claim 6 wherein the composition of the ternary solid solution isabout 24 mol % of Pb(Ni_(1/3) Nb₁₇₀ )O₃, about 42 mol % of PbTiO₃ andabout 34 mol % of PbZrO₃.
 8. A piezoelectric ceramic material accordingto claim 6 wherein at least one additive is added to the ternary solidsolution in an amount greater than 0.5 wt. %
 9. A piezoelectric ceramicmaterial according to claim 6, wherein said piezoelectric ceramicmaterial has a Curie point of not less than 160° C.
 10. A piezoelectricceramic material according to claim 6, wherein said piezoelectricceramic material has a sintered density of not less than 7.70 g/cm³.